Muffler with sequential expansion chambers

ABSTRACT

A muffler able to greatly reduce the exhaust sound of powerful truck engines without too greatly increasing the back pressure. The large shell is concentric with first, second and third inner pipes that are axially aligned, and are spaced apart by a distance approximately equal to their diameter. The central inner pipe is much longer than the other two and, within the shell, all are perforated. Each one is supported by two annular bafflesupport members. The central innner pipe has its baffles spaced in about one-third of the distance from each end. The axially inner members of each of the two end pairs of baffles are spaced different distances from the axially inner end of their respective inner pipes, that of the third inner pipe being much closer to the end of the shell than the corresponding baffle for the first inner pipe. As a result, the distance between the axially inner baffle of the first pair is closer to its adjacent baffle of the second pair than is the axially inner baffle of the third pair to its adjacent baffle of the second pair. Hence a series of chambers of different sizes are formed. Further reduction of sound is achieved by dividing the inner pipes into radial sectors or by introducing the exhaust gases in a swirl, or by placing a flow restriction at the entrance end to the second pipe.

United States Patent [72] Inventors l-luston R. Marlowe Alameda; Donald L. Stephens, Los Gatos; John B. Selvldge, Fremont, all of, Calif.

{21] Appl. No. 19,935

[22] Filed Mar. 16, 1970 [45] Patented June 22, 1971 [73] Assignee Pacific Car and Foundry Company (Peter-hilt Motors Company Division) Renton, Wash.

[$4] MUFFLER WITH SEQUENTIAL EXPANSION 610,000 10/1948 GreatBritain 104,829 6/1942 Sweden Primary Examiner-Robert S. Ward, Jr. Attorney-Owen, Wickersham & Erickson ABSTRACT: A muffler able to greatly reduce the exhaust sound of powerful truck engines without too greatly increasing the back pressure. The large shell is concentric with first, second and third inner pipes that are axially aligned, and are spaced apart by a distance approximately equal to their diameter. The central inner pipe is much longer than the other two and, within the shell, all are perforated. Each one is supported by two annular baffle-support members. The central innner pipe has its baffles spaced in about one-third of the distance from each end. The axially inner members of each of the two end pairs of baffles are spaced different distances from the axially inner end of their respective inner pipes, that of the third inner pipe being much closer to the end of the shell than the corresponding baffle for the first inner pipe. As a result, the distance between the axially inner baffle of the first pair is closer to its adjacent baffle of the second pair than is the axially inner baffle of the third pair to its adjacent baffle of the second pair. Hence a series of chambers of difierent sizes are formed. Further reduction of sound is achieved by dividing the inner pipes into radial sectors or by introducing the exhaust gases in a swirl, or by placing a flow restriction at the entrance end to the second pipe.

PATENTEDJUNEZ I97] SHEEI 1 BF 4 m OE INVENT8R5. sow a T a JOHN B. S EiVl D E 0 MM 1341;.

ATTORNEYS FIG. 8 FIGQ INVHNTORS HUSTON R. MARLOWE DONALD L. STEPHENS JOHN B. SELVIDGE ATTORNEYS PATENTED JUH22 197:

SHEEI 0F 4 INVENTOR5 HUSTON R. MARLOWE DONALD L. STEPHENS JQHN B. SELVIDGE flweq Q/JM/IL AZ L ATTORNEYS MUFFLER WITH SEQUENTIAL EXPANSION CHAMBERS This invention relates to an improved muffler of the type used in the exhaust system of an engine, especially automotive engines.

The problem of muffiing the noise produced by internal combustion engines has become more and more severe as the engines have increased in power.

The powerful diesel engines used in verylarge trucks illustrate the severity of the problem, for they have been so loud that mufflers have heretofore been unable to reduce the noise level to an acceptable value, for certain engines without creating other unacceptable conditions. For example, California law presently requires that the noise level of trucks not exceed 88 decibels at 50 feet, but prior-art muffler structures could not reach that level of quietness without increasing the exhaust back pressure to an intolerable amount. Cost and size have also been factors, for purchasers of the trucks want to utilize as much as possible of the available space for payloads, rather than to accommodate mufflers, and complicated, expensive structures are undesirable.

The present invention provides a muffler that can be identical in size to the currently used unsatisfactory mufflers, and it is comparable to them in cost. Yet it can meet the legal and prescribed standards when used on many large diesel truck engines, and it does not bring about an excessive back pressure.

We have found that to maintain back pressure within acceptable limits demands small gaps between successive inner pipes and that noise level can be reduced by making the inner pipe in three successive, axially aligned and spaced-apart perforated portions, while providing certain proportions between these inner pipe portions and between their supporting baffles. These relationships are quite important and will be explained below in the detailed description of some examples of preferred embodiments. The operation of the muffler can be further improved, we have found, by combining these principles with means for introducing the gas to the muffler in a swirling stream and by constructing inner pipe with radial sectors, or by placing a flow restriction at the entrance end to the second pipe.

Other objects and advantages of the invention will appear from the following description of some preferred embodimerits.

In the drawings:

FIG. 1 is a view in longitudinal section taken along the line 1-1 in FIG. 2 of a muffler embodying the principles of the invention.

FIG. 2 is a view in section taken along the line 2-2 in FIG. 1.

FIG. 3 is a view similar to FIG. 1 of a somewhat modified form of the invention, showing in broken lines some possible positions for the baffles for the central inner pipe, none of which give as good results as the positions shown in solid lines.

FIG. 4 is a view similar to FIG. 1 showing in broken lines some possible positions for the axially inner baffles of the two axially outer inner pipe sections, none of which gives as good results as the solid-line positions.

FIG. 5 is a view similar to FIG. 2 of a modified form of the invention with the inner pipe sections radially sectored.

FIG. 6 is a view in side elevation of a swirler for use with the muffler of FIG. 1, shown adjacent the inlet end thereof.

FIG. 7 is a view in section taken along the line 7-7 in FIG. 6.

FIG. 8 is a view in side elevation of a modified form of swirler.

FIG. 9 is an end view of the'device of FIG. 8.

FIG. 10 is a view similar to FIG. 1 ofa modified form of the invention showing a flow restrictor placed at the entrance to the secondpipe.

A muffler 10 embodying the principles of the invention is shown in FIGS. 1 and 2. It has a cylindrical metal shell 11 with ends 12 and 13. Three pairs of baffle-and-support members, 14, 15 and 16, 17, and 18, 19 support three successive, axially aligned and spacedapart inner pipes 21, 22, and 23.

Between the first pair of baffles 14 and 15 is an annular chamber 24, the baffle 15 being spaced away from the axially inner end 25 of the first pipe 21, toward the baffle 14, but the chamber 24 is about two-thirds or more as long as the first inner pipe 21. The first inner pipe 21 is relatively short and it has an axially outer imperforate portion 26 that has axial slots 27 enabling a snug press fit with the exhaust pipe 28 which conducts the exhaust gases from the engine to the muffler 10. The axially inner portion 29 of the pipe 21 is perforated by conventionally sized holes 30.

The first inner pipe 21 is spaced apart from the second inner pipe 22 by a gap which preferably is small, for we have found that the back pressure can be kept low by having these gaps small. We have found that it is desirable for the gap to be about the same length as the diameter of the inner pipes, and that it can vary from this with some increase in noise or back pressure, by about plus or minus l0 percent. The gap between the second inner pipe 22 and the third inner pipe may be identical or approximately so.

The second inner pipe 22 is preferably perforated fully between its ends 31 and 32, or substantially so, by the holes 30, for best performance. The baffle 16 is spaced in from the end 31 by about one-third the length of the pipe 22, and the bafi'le 17 is spaced in from the end 32 by about the same distance, so that the baffles 16 and 17 define between them an annular chamber 33 that encircles the center third of the pipe 22, or approximately that much.

The third pair of baffles 18 and 19 surround the third inner pipe 23, and define between them an annular chamber 34. Like the baffle 14, the baffle l9 closes one end of the muffler 10 around the inner pipe. THe baffle 18 is substantially closer to the baffle 19 than the baffle 14 is to the baffle 15; so the chamber 34 is shorter than the chamber 24; in fact the chamber 34 is only about half as large. As a result, the distance between the baffles l5 and 16 which define ends of a chamber 35, is somewhat shorter than the distance between the baffles 17 and 18, which define ends of a chamber 36.

The third inner pipe 23 has ends 37 and 38. An axially inner portion 40 of the third inner pipe 23 is perforated by the perforations 30, while an outer portion 41 has axially extending slots 42 that enable a snug press fit around an exhaust pipe section 43 that conducts the exhaust gases away from the muffler 10.

The baffles 14, 15, 16, 17, I8 and 19 may be standard muffler baffles and each may have a dished generally radial wall 45 between inner and outer axially extending flanges 46 and 47. They may be welded in place.

The perforations 30 and their disposition along substantially the full length of the second inner pipe 22 and along substantially the full length of those portions of the first and third inner pipes 21 and 23 that lie inside the shell 11 are important. Omitting them or substantially shortening the length of the perforated portions by making most or all of any of the pipes imperforate raises the noise level. Note that the perforations do not lie only in the chambers 24, 33, and 34 but also beyond them, and we have found that this structure contributes substantially to the needed reduction in noise level.

The location of the baffles 15, 16, 17, and 18 is likewise of considerable significance, as will now be shown. A typical embodiment of the invention, where the exhaust pipes 28 and 43 and the three inner pipes 21, 22, and 23 are four inches in diameter will serve to illustrate the principles involved. The muffler shell 11 is 9 inches in diameter and about 44 inches long. The perforations may be one-eighth inch in diameter, and they may be located about one-half inch from each other axially and circumferentially. About 10 percent of the surface of the second inner pipe 22 is open area, for example. TI-Ie pipe 22 is preferably spaced about four inches apart from each of the pipes 21 and 23, and the pipe 22 is preferably about 21 inches long with the baffles l6 and 17 each 7 inches apart and 7 inches from each end 31 and 32, in this example (which is offered only as an example, not a limitation of the invention). The pipe 21 may be about 11 inches long with the inner 7 inches perforated, and the baffles 14 and 15 may be about 6 inches apart, at their centers or 5 inches at their outer closest together parts. The pipe 23 may be about l2 inches long, with its inner 8 inches perforated, and the baffles 18 and 19 may be about 2%inches apart at their closest points. All this is by way of example only of one very satisfactory construction.

Now consider FIGS. 3 and 4. FIG. 3 shows a muffler in which the inner pipes 21 and 23 are a little shorter than in FIGS. I and 4, so that the gaps are a little longer, but the structure is otherwise quite similar. Experiments were run on the structure of FIG. 3 in which nothing was changed but the positions of the baffles 16 and 17. The baffle 16 occupied at different times the positions A, B, C, and D, the preferred position C being shown in solid lines while the positions A, B, and D shown in broken lines gave less satisfactory results. The baffle l7 similarly was sometimes at position E and sometimes at its preferred position F. The results of the tests, which tested both the sound level in decibels from the same large diesel en gine and the back pressure are as follows:

TABLE I Total exhaust system back Position of battles Sound level, pressure, decibels inches 16 17 at 50 mercury TABLE II Total exhaust system back Position of baffles Sound level, pressure, decibels inches at 50 mercury We have found also that the noise level can be reduced about one decibel further, without raising the back pressure too much by using the structure shown in FIG. 5 for providing each of the inner pipes 21, 22, and 23 throughout the length of each with radial compartment walls 50. There can be four or,

better, six such walls 50, and these walls can be made from a flat strip 51 to which are welded two 60 angles 52, each bent from a similar strip.

Further noise reduction with only minor increase in back pressure can be obtained by causing the exhaust gas to enter the muffler in a swirling manner. The structure of FIGS. 6 and 7 employs four helical segments 55, 56, 57, and 58 at the entrance to the muffler 10, in or just before the first inner pipe 21. Tile structure of FIGS. 8 and 9 uses a series of flat vanes 60 welded to a cylindrical member 61 that follows an upstream cone 62. The vanes are welded at an inclination to impart the swirling. Other similar structures may be used.

FIG. 10 shows a muffler similar to that of FIG. 1 but having a flow restriction at the entrance end to the second pipe 22. The restriction may be provided by a tubular member 70 having a wide portion 71 and a narrower portion 72 joined to the wide portion by a step portion 73. This expedient helps to reduce sound and is an alternate to the expedients shown in FIGS. 69.

To those skilled in the art to which this invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.

We claim:

1. A muffler for connection between first and second exhaust pipe sections of an engine, including in combination:

a tubular shell about twice the diameter of said exhaust pipe sections,

first, second, and third inner pipes substantially identical in diameter to said exhaust pipe sections and axially in line with each other, in and concentric with said shell imperforate end portions of said first and third inner pipes projccting beyond the ends of said shell for connection respectively to said first and second exhaust pipe sections, said second inner pipe and the portions of said first and third inner pipes that lie axially within said shell being perforated, said inner pipes being spaced apart from each other successively by first and second gaps, each about as long as the diameter of said inner pipes, and

first, second, and third pairs of annular baffle and support members secured to both said shell and, respectively to said first, second, and third pipes to hold them in position in said shell and to provide annular chambers therearound and to divide said chambers from each other,

the axially outer members of said first and third pairs closing the space between said shell and said first and third inner pipes at the ends of said shell, the axially inner members of said first and third pairs being spaced away from the axially inner ends of said first and third inner pipes toward said outer members, the inner member of said third pair lying substantially closer to the outer member of said third pair than the inner member of the first pair lies to the outer member of said first pair,

said first inner pipe and said third inner pipe being approximately of the same length, while said second inner pipe is approximately twice as long as the portions of said first or third inner pipes that lie axially within said shell,

said second pair of baffle and support members each lying at about one-third of the length of said second inner pipe, so that between them they define a chamber around the middle third of said inner pipe, said members of said second pair lying at different distances from said inner members of said first and third pairs, to define end walls of chambers of different length.

2. The muffler of claim 1 wherein said inner pipes are each divided into a plurality of sectors by generally radially extending partitions.

3. The muffler of claim 1 having means for causing the exhaust gases from said first exhaust pipe section to enter into said first inner pipe with a swirling motion.

4. The mufi'ler of claim 3 wherein said means for causing comprises inclined radially extending vanes.

5. The muffler of claim 3 wherein said means for causing comprises generally helically twisted vanes.

6. The muffler of claim 1 wherein the entrance to the second pipe is made smaller'by partial obstructions at that point. I

7. A muffler for connection between first and second exhaust pipe sections of an engine, including in combination:

a tubular shell about 2.5 times the diameter of said exhaust pipe sections,

first, second, and third inner pipes substantially identical in diameter to said exhaust pipe sections and axially in line with each other, in and concentric with said shell, imperforate end portions of said first and third inner pipes projecting beyond the ends .of said shell for connection respectively to said first and second exhaust pipe sections, said second inner pipe and the portions of said first and third inner pipes that lie axially within said shell being perforated, said inner pipes being spaced apart from each other successively by first and second gaps, each within percent as long as the diameter of said inner pipes, and

first, second, and third pairs of annular baffie and support members secured to both said shell and, respectively to said first, second, and third pipes to hold them in position in said shell and to provide annular chambers therearound and to divide said chambers from each other the axially outer members of said first and third pairs closing the space between said shell and said first and third inner pipes at the ends of said shell, the axially inner members of said first and third pairs being spaced away from the axially inner ends of said first and third inner pipes toward said outer members, the inner member of said third pair lying substantially closer to the outer member of said third pair than the inner member of the first pair lies to the outer member of said first pair,

said first inner pipe and said third inner pipe being approximately of the same length, while said second inner pipe is approximately 2.3 times as long as the portions of said first or third inner pipe that lie axially within said shell,

said second pair of bafi'le and support members each lying at about one-third of the length of said second inner pipe, so that between them they define a chamber around the middle third of said inner pipe, said members of said second pair lying at different distances from said inner members of said first and third pairs, to define end walls of chambers of different length.

8. The muffler of claim 7 wherein said inner pipes are each divided into a plurality of sectors by generally radially extending partitions.

9. The m uffler of claim 7 wherein the entrance to the second pipe is made smaller by partial obstruction at that point.

10. The muffler of claim 7 wherein the partial obstruction passage therethrough. 

1. A muffler for connection between first and second exhaust pipe sections of an engine, including in combination: a tubular shell about twice the diameter of said exhaust pipe sections, first, second, and third inner pipes substantially identical in diameter to said exhaust pipe sections and axially in line with each other, in and concentric with said shell imperforate end portions of said first and third inner pipes projecting beyond the ends of said shell for connection respectively to said first and second exhaust pipe sections, said second inner pipe and the portions of said first and third inner pipes that lie axially within said shell being perforated, said inner pipes being spaced apart from each other successively by first and second gaps, each about as long as the diameter of said inner pipes, and first, second, and third pairs of annular baffle and support members secured to both said shell and, respectively to said first, second, and third pipes to hold them in position in said shell and to provide annular chambers therearound and to divide said chambers from each other, the axially outer members of said first and third pairs closing the space between said shell and said first and third inner pipes at the ends of said shell, the axially inner members of said first and third pairs being spaced away from the axially inner ends of said first and third inner pipes toward said outer members, the inner member of said third pair lying substantially closer to the outer member of said third pair than the inner member of the first pair lies to the outer member of said first pair, said first inner pipe and said third inner pipe being approximately of the same length, while said second inner pipe is approximately twice as long as the portions of said first or third inner pipes that lie axially within said shell, said second pair of baffle and support members each lying at about one-third of the length of said second inner pipe, so that between them they define a chamber around the middle third of said inner pipe, said members of said second pair lying at different distances From said inner members of said first and third pairs, to define end walls of chambers of different length.
 2. The muffler of claim 1 wherein said inner pipes are each divided into a plurality of sectors by generally radially extending partitions.
 3. The muffler of claim 1 having means for causing the exhaust gases from said first exhaust pipe section to enter into said first inner pipe with a swirling motion.
 4. The muffler of claim 3 wherein said means for causing comprises inclined radially extending vanes.
 5. The muffler of claim 3 wherein said means for causing comprises generally helically twisted vanes.
 6. The muffler of claim 1 wherein the entrance to the second pipe is made smaller by partial obstructions at that point.
 7. A muffler for connection between first and second exhaust pipe sections of an engine, including in combination: a tubular shell about 2.5 times the diameter of said exhaust pipe sections, first, second, and third inner pipes substantially identical in diameter to said exhaust pipe sections and axially in line with each other, in and concentric with said shell, imperforate end portions of said first and third inner pipes projecting beyond the ends of said shell for connection respectively to said first and second exhaust pipe sections, said second inner pipe and the portions of said first and third inner pipes that lie axially within said shell being perforated, said inner pipes being spaced apart from each other successively by first and second gaps, each within 10 percent as long as the diameter of said inner pipes, and first, second, and third pairs of annular baffle and support members secured to both said shell and, respectively to said first, second, and third pipes to hold them in position in said shell and to provide annular chambers therearound and to divide said chambers from each other the axially outer members of said first and third pairs closing the space between said shell and said first and third inner pipes at the ends of said shell, the axially inner members of said first and third pairs being spaced away from the axially inner ends of said first and third inner pipes toward said outer members, the inner member of said third pair lying substantially closer to the outer member of said third pair than the inner member of the first pair lies to the outer member of said first pair, said first inner pipe and said third inner pipe being approximately of the same length, while said second inner pipe is approximately 2.3 times as long as the portions of said first or third inner pipe that lie axially within said shell, said second pair of baffle and support members each lying at about one-third of the length of said second inner pipe, so that between them they define a chamber around the middle third of said inner pipe, said members of said second pair lying at different distances from said inner members of said first and third pairs, to define end walls of chambers of different length.
 8. The muffler of claim 7 wherein said inner pipes are each divided into a plurality of sectors by generally radially extending partitions.
 9. The muffler of claim 7 wherein the entrance to the second pipe is made smaller by partial obstruction at that point.
 10. The muffler of claim 7 wherein the partial obstruction comprises an annular member reducing the diameter of the passage therethrough. 